Nowadays low range FM radio transmitters are commonly used for transmitting e.g. music which is stored in the memory of a device, which is equipped with such a FM transmitter. The music or other audio content is transmitted to a users car radio or home stereo equipment for reproduction by this equipment. Such kind of FM transmitters might be stand alone FM transmitters with integrated memory for storing music or the FM transmitter includes an interface for connection to an external memory. The FM transmitter my also be integrated into mobile communication devices, such as mobile phones incorporating a memory which stores e.g. music for playback.
FM transmitters were historically not allowed in many countries some time ago because they transmit FM radio signals like any FM radio broadast station in the same frequency range in order to facilitate receiption of the transmitted signal by standard FM radio receivers. During the last couple of years FM radio transmitters were allowed for private use but they need to fulfill certain regulatory requirements in order not to interfere with each other and particularly not interfere with FM broadcast radio stations and other telecommunication systems.
The legal status of FM transmission varies around the world today and its limits of operation set by the regulatory bodies differ from country to country, e.g. while some countries do not allow FM transmission, the power is limited to 50 nW by ETSI (European Telecomunications STandardisatin Institute) in Europe, 250 uV/m@3 m by FCC (Federal Communication Commission) in the USA, and recent regulations in China limit the output power of FM transmitters to 45 nW ERP (Effective Radiated Power.